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Distribution of biomarkers in lacustrine sediments of the Linxia Basin, NE Tibetan Plateau, NW China: Significance for climate change
作者: Y. L. Wang, X. M. Fang, T. W. Zhang, Y. M. Li, Y. Q. Wu, D. X. He, Y. Gao, P. Meng and Y. X. Wang
期刊名称: Sedimentary Geology
发表年度: 2012
卷: 243
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页码: 108-116
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全文链接: http://dx.doi.org/10.1029/2011jd015921
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摘要: In this study, n-alkanes, isoprenoids and n-alkyl-ketones were detected in lacustrine sediments in the Maogou section of the Linxia Basin, NE Tibetan Plateau, NW China. The distribution characteristics of these compounds correspond to arid climate change in inland Asia from the upper Oligocene to the Pliocene. The characteristic bimodal distribution of n-alkanes, which was observed in the investigated samples, is centered on n-C-17-n-C-20 and has maximum values at n-C-18 in all samples; n-C-27-n-C-31 has maximum values at n-C-29 in some of the samples. The front mode shows a weak even carbon number predominance of short-chain n-alkanes (CPI17-21 0.55-0.89); in contrast, the back mode has a strong odd carbon number predominance of long-chain n-alkanes (CPI25-31, 1.41-2.42). Changes in the nC(27)/nC(31) ratio (woody plants/grassy plants) along the entire section corresponded to three climate stages: an arid to humid climate stage from similar to 22.5 to 18.4 Ma; 6.25 to 5.5 Ma; and two major humid stages at similar to 18.4 Ma and similar to 5.5 Ma. A warm-humid climate was identified for the similar to 10 Ma to similar to 9 Ma period, which turned to an arid-cold climate from similar to 8 Ma to similar to 7.5 Ma, by assessing changes in the (n-C-17-n-C-21)/(n-C-27-n-C-31) ratios. Warm-humid conditions gradually increased from similar to 7.5 Ma to similar to 5.5 Ma, as has been confirmed by multiple geochemical climate indicators. A distinctive climate change toward arid-cold conditions at similar to 8 Ma corresponded to a striking increase in the high-carbon-numbered n-alkanes and a rapid decrease in the (n-C-17-n-C-21)/(n-C-27-n-C-31) and n-C-27/n-C-31 ratios of n-alkanes, which suggests a large input of higher plants. Our observation from the biomarker analysis is in agreement with previous reports that used palynofloras to determine that climate change in the investigated region responded to the uplift of the Tibetan Plateau at similar to 8 Ma. (C) 2011 Elsevier B.V. All rights reserved.
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